The state of the art includes rolling rolls which include counter-opposed working rolls, respectively upper and lower, defining the rolling plane and mounted on relative chocks, arranged on one side and the other of the rolling stand.
In four-high rolling stands the working rolls cooperate with respective upper and lower back-up rolls, which are also mounted on relative chocks arranged on one side and the other of the rolling stand.
In four-high rolling stands, the state of the art includes an embodiment where the chocks of the back-up rolls laterally contain, at least partly, the chocks of the relative working rolls.
In the state of the art, it is known that the working rolls need to be removed periodically from the rolling stand in order to replace them or to grind the surface.
The operation to remove the working rolls normally comprises a procedure to release the chocks from the housing of the stand followed by the axial removal of the rolls from the rolling stand.
For a four-high rolling stand where the chocks of the back-up rolls contain the chocks of the working rolls, there are different systems to remove the rolls which, however, have shown themselves to be complex to operate and/or bulky and/or not economically viable.
Among these there is a system which provides to use movable rails suitable to move from a lowered position of no contact, outside the rolling stand, to a raised working position, inside the rolling stand, and vice versa.
These rails cooperate with a roll removal plane arranged outside the rolling stand.
In the working position the movable rails come into contact with the chocks of the lower working roll and raise them by a desired value so that the chocks can be axially removed, with the relative rolls, from the rolling stand.
On the lower face of the chocks of the lower working roll there are advantageously included sliding means suitable to cooperate with the movable rails.
During the removal step the lower working roll is temporally constrained to the upper working roll, for example by means of a temporary clamping of the respective chocks, so as to achieve a single block which makes it possible to remove both rolls in a single operation.
This solution, although it is widely appreciated because it allows the rolls to be removed without altering the configuration of the rolling stand, has some disadvantages.
A first disadvantage is that it is necessary to use assemblies to move and lift the rails, and also the relative supports, which are very strong so as to be able to support the highly cantilevered loads to which the moving and lifting assemblies are subjected during the lifting and removal of the chocks and rolls.
In fact, the lifting assemblies, consisting for example of jacks, screws, driven sliders etc., are located outside and on the side of the stand and are introduced inside the stand during the replacement step, with an axis at least partly oblique with respect to the vertical development of the stand.
Moreover, moving the rail at a direction which is oblique to that at which the rolls are removed entails high friction forces which cause premature wear and over-sizing.
A further disadvantage is the large amount of space occupied outside and at the side of the stand.
Furthermore, the arrangement and the structure of the lifting assemblies entail considerable difficulties in maintenance.
The state of the art also includes devices wherein the sliding rails are always arranged inside the space occupied by the chocks of the lower working roll.
DE-A-2.344.166 discloses a device to lift the working rolls of a four-high rolling stand, the device comprising a pair of levers (19) for each of the rails, suitable to be made to rotate by outer actuators (14) arranged at the sides of the stand.
The actuators (14) are inclined with respect to the plane on which the rolls to be lifted lie.
This embodiment has the disadvantage that the mechanical parts are subjected to considerable stress due to the fact that the lifting devices do not act in line with the loads to be lifted and supported.
Moreover, it requires complex operations on the chocks in order to install the device. Furthermore, the system must necessarily conform to the diameters of the working rolls and the back-up rolls.
In GB-A-2.094.684, the system to lift the rails used to remove the working rolls comprises actuators (11) installed on board the chocks of the back-up rolls.
The system is very complex, since in order to lift the rails the actuators lift the chock of the lower back-up roll and at the same time determine the action of an L-shaped lever on a protrusion solid with the rails.
Moreover, the system requires special work to be installed and is expensive since every chock has its own actuators.
Furthermore, since it is installed on board the chocks, the system has to conform to the diameters of the working and back-up rolls.
U.S. Pat. No. 3,638,467 describes a removal system for working rolls wherein stationary rods (14, 16) are used, with the function of distancing, automatically and constantly, the chocks of the working and back-up rolls.
This document does not explain how the rails are lifted.
In any case, this document does not provide actuators inside the bulk of the rolling stand and suitable to lift the rails from their low position, as shown in FIG. 4, to the high position shown in FIG. 3 wherein they cooperate with the chocks of the lower working roll.
The present Applicant has designed, tested and embodied this invention to overcome these shortcomings and to obtain further advantages.